In the past, standard superheterodyne or regenerative transmitter/receiver systems, while having great range, have had drawbacks which caused them to have high current drains and be large in size. This is not required and often undesirable for transmitters and receivers used, for example, in paging systems or for remote actuation of, for example, garage doors or camera remote flash synchronizers, or security alarm systems. In such prior transmitter and receiver systems, two or more piezoresonators are used to establish a channel for existing paging and channelized radio links. The simultaneous transmission of two or more frequencies superimposed on a carrier are amplified, detected and used to activate these piezoresonators to establish the existence of the desired channel. The number of channels is thereby limited to the number of discrete specific piezoresonators or mechanical filters responding to the impressed set of received signals.
A large amount of power is used in such systems, both in establishing the transmitting carrier, modulating this carrier, and providing standby current in receivers using local oscillators. The end result is a requirement of a large battery capacity or other power supply employing, e.g., a transformer, large size, and limited channels with large piezoresonators.
In addition, radio transmitters having average peak power above certain limits are regulated by the federal government. This has created, along with the size and power supply constraints, certain range limits on, e.g., transmitters used for garage door openers, and has required licensing of paging systems having ranges of, e.g., a few miles. By way of example, present garage door openers are specified to have about a 150-foot range, whereas many applications thereof require longer ranges. There is therefore, a great need for transmitter/receivers which can carry information in a plurality of short bursts of pulses having individually high peak power for greater range, but together having a relatively small average peak power over the duration of the plurality of pulses in the burst.
There exists a need for a micro, i.e., miniaturized radio link that can operate on extremely low power in the standby mode and be field programmable with multiple channels for communications or remote control. Up to now, existing radio frequency links required relatively large amounts of power and were quite bulky. The present invention relates to a transmitter and receiver capable of miniaturization and micro-power operation, both for the transmitter and the receiver. The present invention has many useful applications, such as providing radio links to be incorporated in very small housings, for example, the size of a button or key chain for use, for example, with paging receivers and garage door openers, respectively. The present invention could also be used for applications such as electronic door locking devices and, for example, activating remote camera flash units or remote alarms in a security alarm system, coded to the location of the security breach.
The receiver of the present invention is quite small in comparison, e.g., to prior garage door openers, which require, e.g., transformers in their power supply, in order to operate. Thus the receiver of the present invention will decrease significantly the size and cost of a garage door opener receiver, and also is suitable in size for placement, e.g., within a door or door frame for use in an electronic key locking system or on a remote camera flash unit for remotely activating the remote camera flash unit. In fact, the receiver of the present invention could be miniaturized enough to be placed in a coat button or lapel pin in the paging embodiment or even incorporated in a wristwatch housing, employing, e.g., the alarm on the wristwatch as the paging enunciator. In certain applications, for example, remote photo flash operation, the receiver can be connected to the remote flash unit and use the battery or other power source already contained in the flash unit for its power source, if such a flash unit is of a type having a sufficient voltage available across its actuator switch contacts, thereby eliminating any requirement for a power source in the receiver unit itself.
The problems existing in the prior art enumerated in the foregoing are not intended to be exhaustive, but rather are among many which tend to impair the effectiveness of previouslyknown transmitter/receivers used, for example, in paging units, garage door openers, electronic locks, security alarms or remote photographic equipment operation. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that prior transmitter/receiver units of the foregoing-mentioned type appearing in the art have not been altogether satisfactory.
Recognizing the need for an improved transmitter/receiver useful for such applications as paging units, garage door openers, electronic keys or remote operation of, for example, photographic equipment, it is, therefore, a general purpose of the present invention to provide a novel miniaturized transmitter/receiver which minimizes or reduces the problems of the type previously noted.
An additional feature of the present invention is a radio transmission link having a relatively great range in comparison to its average peak power.
A further feature of the present invention is the use of integrated circuit chips in the transmitter and receiver to modulate the transmitted frequency into a plurality of pulses of a selected pulse width and duration and the detection in the receiver of a received signal having the selected pulse width and pulse duration in order to activate some remote unit, e.g., a paging enunciator, garage door opener, electronic door lock, security alarm or photographic flash equipment.
Still another feature of the present invention is the ability to select a wide variety of channels by varying the selected pulse width, and tuning the receiver to be selective of only that pulse width, within certain tolerances.
The present invention relates to a transmitter/receiver employing suitable microchip circuitry to pulse modulate a transmitted, e.g., radio frequency, signal and to demodulate the received signal to detect for a selected pulse width in the transmitted signal, thereby enabling coding of selected channels. The transmitted pulses can be made to have a sufficient peak power to enable transmission of a burst of such pulses of, e.g., 20-30 in number over a range of up to about five to ten miles, but of a sufficiently short individual pulse duration, with a sufficiently long pulse interval, that the average peak power is relatively very small, for example, with a 10 watt peak power in each of 20-30 pulses transmitted within less than a millisecond and with each pulse having only a 10-20 microsecond duration, the average peak power would be less than a milliwatt. The transmitter uses a pair of coupled monostable multivibrators contained on an integrated circuit chip to fix a pulse duration and pulse interval for a plurality of pulses of, e.g., radio frequency, energy, which radio frequency energy is generated in each pulse width by a resonating tank circuit, with the resonation being rapidly clamped to ground at the end of each pulse width. The receiver amplifies and demodulates the received pulses to obtain a plurality of pulses having the pulse width and pulse interval of the received signal with the higher, e.g., radio frequency removed. This plurality of pulses is fed to a pair of coupled monostable multivibrators contained on an integrated circuit chip. The pair of monostables act as a portion of a pulse coincidence circuit. Each generates a coincidence pulse. One monostable generates a coincidence pulse at one transition of each received pulse from one of the two states of each received pulse to the other state. The other monostable generates a coincidence pulse, after a selected time interval from a transition from one state to another of each received pulse. The time interval is selected so that at a given pulse width of the received pulses, within certain tolerances, there will be coincidence of the coincidence pulses. Such coincidence is detected and after a selected number of such coincidences within a selected time period, a trigger circuit in the receiver is actuated.